Joe Ricky Hundley, of Hayden, Idaho, pleaded not guilty Wednesday in federal court, The Atlanta Journal-Constitution reported.
Hundley was arrested following the incident aboard Delta Flight 721 from Minneapolis to Atlanta Feb. 8.
The toddler's mother, Jessica Bennett, told the FBI in Atlanta Feb. 12 her 19-month old son, Jonah started to cry because of cabin pressure and said Hundley, who was sitting next to her, told her to "to shut that [racial slur] baby up" before he slapped the boy in the face.
At a hearing Wednesday, Hundley's attorney Marcia Shein said her client admitted using a racial slur, WSB-TV, Atlanta, reported.
"He was traveling from Minneapolis to Atlanta to decide to take his only child and son off of life-support, he was under a great deal of stress, he was very grieved and had been up for the prior 24 hours. When this happened, my client said something inappropriate to Mrs. Bennett, something he shouldn't have said even in his darkest hour. We hope for Mrs. Bennett's sake and my client's sake that everyone will forgive him for what he said," Shein said.
Shein said Hundley's son overdosed on insulin and died several days after the incident on the plane.
Hundley was fired after the incident from his job at Aerospace and Defense, Composite Group, which provides technology and other services for the military and businesses.